Petroleum refining



w. A. CRAIG ETAL ATTORNEYS Patented June 2, 1942 Wallace A. Craig Calif.,` assignors .u Los.Angeles,Calt.,.

and Pani C. Rich, Los Angeles, to Richield Oil Corporation, a corporation Vof Delaware 'Appreciate Februaryiv, 1940; serial No. 319,437

sonnesl (Vol. 19e- 41) u This invention is concerned with the prevention of corrosion of` vessels employed in` handling petroleum products in oil reineriesand the like, and contemplates the treatment of certain types of petroleum products, such asfsoui` gasoline; to extract therefrom aliphatic acids containing not to exceed six carbon atomsper molecule, for example, formic, acetic, and propionic acids and the butyric and the valerie acids. Such acids tend to form throughside Areactions which occur during the cracking of petroleum from Vsome iields and exert a powerful corrosive actionon iron and steel c'zontainers and conduits and also exert a deleterious eiiect in certain present day petroleum reiningprocesses.

We have discovered that raw gasoline and other relatively low-boiling petroleum v'products petroleums, for examformed 'by cracking some ple, certain Los Angeles Basin Crude Oils, exert a powerful corrosive iniiuenceY upon iron and other metals with which they come in contact. The corrosive tendency of these products is due to a relatively small but exceedingly'active proportion of' aliphatic acids having not more than six carbon atoms per molecule 'and exemplified by formic`,facetic andp'ropionic acids andthe butyric and the valerie acids. 'These acids are. formed in the petroleum products during cracking and are miscible with' and are dissolved vin the lower-boiling products of thecracking (such as gasoline) `at the concentration at which these acids are produced. In large part, lthe acids distill with that fraction of the products that boils below about 200 F. and becomeV concen- 'trated in this fraction. It 'is with this fraction that corrosion diiiiculties are serious. V,The acids, in the presence of a small proportion of' Water almost inevitably contained in the fraction, exert a strong corrosive influence; Moreover, -the acids containedin thisiiraction cause diiiiculty in subsequent reiiriingY steps. Thus, these acids may bring about serious ccrrosionat all points in a modern petroleum refinery from the-bubble tower in the cracking section from which crude gasoline is derivedthrough the Various refining steps until 'they are either removed from the system or are neutralized in. `some specific operation. We have, for example'experienced degradation of tri-potassium phosphate solution, used `for removing. the hydrogen sulfide fromV the gaseous charge to the-polymerization unit, due to the reaction of the tri-potassium phosphate with the organic acids. This is objectionable and Acany be avoided by the practice of our'invention.

As a result of our investigations, we havevdis covered that the corrosiveaction of sour gaso lines and other low-boiling mixtures of yhydrocarbons containing some Water jplus aliphatic I: acids or six or less carbon atoms per molecule is substantially reduced'by Washing the gasoline or the like with water or other aqueous body. Water alone serves to extract the acids, par

ticularly those having fewer carbon atoms per Vheavier acids, however', may be extracted i.V e., there is a decrease molecule. Thus, by washing with water or equivaient non-alkaline aqueous fluid, substantially all of the formic and acetic acids can be extracted from raw gasoline. `The Water also tends to extract Ythe higher acids butless thoroughly,

in thegeiciency of eX- traction of propionic acid,` the butyric acids and the valerie acids in the order named. These with substantial completeness Yby subsequently washing the gasoline orother product with an 'aqueous alkaline solution, but from the standpoint of corrosion reduction, such additional Washing is sel- .dom necessary, for

' after, preliminary fractionation the higher acids appear to be; more sluggishlin their corrosive action.v The acidA content extractable by Water aloneisthat which otherwise would bring about intolerable corrosion. A p l ,In accordance with our invention, the water washing should` be conducted, in a petroleum re fineryv where the acids occur, as early as possible has concentrated the aliphatic acids in the 10W-boiling fraction of hydrocarbons. In other words,v maximum adn vantage in the use of our invention is gained through extractingv the acids as soon as possible after they have been formed and have had an opportunity to associate with water and gain an objectionable concentration. Thus, We have found that raw gasoline and lighter hydrocarbons formed directly through cracking (or by the al-V kylation or polymerizationA of lower hydrocarbons, including some that have resulted from cracking.)` should be treated as early in the process as possible in order to extract the acids.

Single stage washing With Water at atmospheric temperatures will in most cases extract Vrent series,` accomplishes a more thorough re movalof the acid and is desirable when the acids are recovered for use or when singleY stage washing does' not sufficiently inhibit corrosion.

Almost any type of scrubbing equipment that will assure adequate contact of water and the petroleum product being treated may be used. Thus, the water may be permitted to percolate downward through a large tank of raw gasoline. However, it is preferable to employ agitators or other apparatus to assure adequate mixing of the gasoline and the water, followed by a settler of conventional type from which the washed gasoline is decanted. Washing of the gasoline or other hydrocarbon product in the vapor phase may be accomplished in a tower or the like in which the vapors pass countercurrent'to the water. Y y

We have found that more eincient washing (from the standpoint of water, consumed) and a stronger aqueous solution of the acids may be obtained by circulation of the wash water, and that a substantial concentration of the acids in the water may be built up through such circulation without serious effect upon the degree of extraction. 'I'he dilute acid solution which is separated from the gasoline may be` treated to obtain a more concentrated form of the acid or to separate the various acids from each other. This may be accomplished by fractional distillation.

Whether or not a product of petroleum cracking will contain initially the aliphatic acids with which We are concerned depends, we believe, principally upon the nature of the petroleum, which, in turn, is dependent upon the eld from which it is produced. Thus, crude oil from the Wilmington (California) eld is converted by cracking into products containing substantial proportionsof these acids. The same is Vtrue with respect to crudes from 'other fields in the Los Angeles basin. On the other hand, crudes from elds in certain other sections of the country do not yield products containing appreciable quantities of theseacids even though subjected to cracking and subsequent treatment in identical apparatus. In no instance, so far as we are aware, is there a large proportion of such acids in the petroleum product, and it might well be supposed that the small amount present would have no harmful effect. The fact is, however, that in the presence of the water which almost inevitably occurs in at least a small proportion in the products of pyrolytic cracking, the

acids exert a profound corrosive inuence. Thus.,

a sour gasoline containing 0.01 mol per liter of aliphatic acids brings about serious corrosion of refinery equipment.

To take a typical example, the total acid content (0.01 mol per liter of distillate) of a sour gasoline may be divided as follows:

Table l Portion of Approximate Acid ingredients total content per 1 000 acidity bbl. of gasohne Per cent Pounds44 25 Forrnio acid. Acetic acid..h 55 57. 75 Propionic acl 18 23. 25 Butyric acids 27. 70 Valerio acids and heavier 27 96.25

It will be observed that even with such a small proportion of total acid in the gasoline, the total Weight of the acids in the total gasoline production of a large renery is substantial. In fact, gross value of the acids extractable by water washing from a gasoline of the above type is, based upon recent market quotations, approximately $11.25 per 1000 bbl. of gasoline produced.

The eiiciency of extraction of the lighter and heavier acids by water washing of various types is given in the following table: l

Table II Percent of original acid remaining in gasoline Type oi wash used Propionic Iso-butyric Acetic acid acid mid 1 stage:

5% wash water 10g, wash water. 20 a wash water.

2 countercurrent stage 5% wash water 10% wash water..- 20% wash water- 3 countercurrent stages.

5% wash water 1 10% wash water 20% wash water In the foregoing table and hereinafter the percentages of wash water are calculated on the Volume of the gasoline washed.

The various washing procedures, the results of which are tabulated above, employed water at approximately atmospheric temperature and an eiort was made to mix gasoline and water thoroughly in each stage, mixing being followed by settling and decantation of the gasoline. It will be observed that acetic acid is extracted relatively thoroughly in a single washing stage with as little as five per cent (5%) wash water on the volume of the gasoline, and that extraction of acetic acid is not improved substantially by employing more than 2 countercurrent washing stages with ten per cent (10%) wash water in each stage. Formic acid is, like acetic acid, thoroughly extracted with but a slight water treatment. Propionic acid, on the other hand, can be extracted thoroughly by water washing but requires a prolonged treatment. Thus, single stage washing with ve per cent (5%) Wash water leaves 64 per cent of the propionic acid in the gasoline and an extraction of 97 per cent of the propionic acid is not obtained until it has been washed in 3 countercurrent stages with twenty per cent (20%) by volume of Wash Water.

Washing treatment that will extract substantially all of the acetic and formic acids and a reasonably large proportion of the propionic acid will leave most of the butyric acids and heavier acids in the gasoline. Thus, 3 stage countercurrent washing employing twenty per cent (20%) of Wash water will extract in excess of 99 per cent of the acetic acid and 97 per cent of the propionic acid but will leave 64 per cent of the iso-butyric acid unextracted. Less thorough washingprocedure will leave an even larger percentage of iso-butyric acid in the gasoline, and it is possible to conserve 91 per cent of the iso-butyric acid while extracting 98 per cent of the acetic acid, and 50 per cent of the propionic acid, this being accomplished in 2 countercurrent washing stages employing five per cent (5%) by volume of wash water.

The overall extraction eflciency of the Various acids from the distillate by the Various wash- `ing procedures described 4maybe Valeric acids and heavier above has the following acid content:

follows:

" Table III corrosion difficuiueswfoi1owing the debutamzer can be completely eliminated by subjecting only the overhead of the debutanizer to water washing. This washing can `be conducted either with l Percent of 5 thehydrocarbons in liquid phase or vapor phase. Since the debutanizer overhead y is normally gaseous, it may be advisable to wash it in vapor phase,` employing f a scrubbing tower through Vwhich the 'vapors Vpass in countercurrent to' a water wash.

If the lighter acids are extracted from the debutanizer overhead or other light fraction, the

' other and heavier acids which have commercial value but which do notbring about excessive corrosion, may be extracted from the heavier fraction or from merged gasoline products following polymerization or the like. The extraction by washing with alkali of propionic and butyric acids is described in detail in our cooriginalV acids rev maining in product after washing.

46. 6 4i. 3 20% 37. 4 2 countercurrent stages:

5% wash water 40. 8 wash water 37. 1 15 wash weten 34. l 3 countercurrent stag i 67 wash water.. 39. 8 l0 awashw er 36.3 20 a wash water i 33. 5

The relatively poor attractionby water alone of the acids of higher molecular weight accounts for the relatively large percentage of the original aliphatic acid content of hydrocarbon that remains after washing. However, from the standpoint of corrosion, it is unnecessary to carry out water washing tovextract more than sayv about 60 per cent of the total acids. Thus, employing 2stage 'countercurrent washing, applying iive per cent (5%) wash water on the volume of the product being washed, the following results are obtained` in washing a cvracked distillate containing .01 mol total aliphatic. acids per liter. On this basisa wash water of the following analysis is formed:

Table V Acids inthe water wasn4 (basis 5o bbl. wate'r/y 1000 bbl. of gasoline) Lb./bbl. of water Formic acid 0.0539N `13.9 Acetic acid 0.0539 18-.1 Propionic acid 0.0090 3.7 Butyric acids-; 0.0016 0.8

The total residual acid in the washed cracked v distillate following the 2 stage washing outlined Table V Residual acid in the washed cracked distillate= 0.00408N containing Lim/1000 bbl. 0f 011 the gasoline or other pending application Serial No. 319,436, iiled February 1T, 1940, and is shown diagrammatically on the accompanying flow sheet which also illustratesV the'preliminary water washing described above for the selective removal of formic and acetic acids.

We claim:

1. In the treatment of a petroleum hydrocarbon product containing iormic acid, acetic acid and a butyric acid, said treatment involving contact ofthe hydrocarbon product with metal, the

Y improvement which comprises washing the product with water until a relatively large proportion of the formic acid and the acetic acid are extracted while a relatively large proportion of the butyric acid is left inthe product, thereby reducing the corrosive action of the product upon the metal in the presence of water.

2. In the treatment of a petroleum hydrocarbon product containing formic acid, acetic acid and a butyric` acid, the improvement which comprises subjecting the product to fractional distillation to vaporize and separate a fraction Formic acid 0.000055N 0.875 Acetic acid'. 0.000055 i 1.125 Propionic acid 0.00045 11.625 Butyric acids 0.00082 25.250 Valerie acids and heavier 0.00270 96.250

Since corrosion is principally due to the'acids of lower molecular weight, say iormic acid and acetic acid, extraction of these acids alone while leaving the heavier acids in the distillate `for subsequent extraction by alkali washing is desirable. We have discovered that a large proportion of the formic acid and the acetic acid, and a smaller proportion of the propionc acid tends to distill with a very light fraction of the cracked hydrocarbons driven ofi during stabilization treatment, i for example, the overhead product of a debutanizer comprising butane, isobutane, and lighter hydrocarbons that are normally gaseous.

Thus,

containing` low-boiling hydrocarbons and the formic and acetic acids while leaving a large proportion vof the butyric acidl in the residual liquid and subjecting the fraction thus separated to Water washing to extract the formic and acetic acids therefrom, whereby the corrosive action of the fraction and of the residual liquid upon metals in the presence of water is reduced.

3. In the treatment of a petroleum hydrocarbon product containing a relatively small proportion of water and formic acid, acetic acid, propionic acid and a butyric acid, which treatment involves contact of the hydrocarbon prodwhich comprises washing the product with a relatively large volume of water until a substantial proportion of the forrnic acid, acetic acid and propionic acid has been extracted from the product while leaving a large part of the butyric acid therein, and thereafter separating the wash water from the hydrocarbon product thereby reducing the corrosive activity of the latter.

4. In the treatment of a petroleum hydrocarbon product containing formic acid, acetic acid, propionic acid and a butyric acid, the improvement which comprises subjecting the hydrocarbon product to water washing until alarge proportion of the orrnic acid andthe acetic acid and a smaller proportion of the propionic acid has been extracted, the butyric acid in large part carbon product, and treatingthe hydrocarbon product thus separated with an alkaline aqueous solution to extract the butyric acid therefrom.

5. In the treatment of a petroleum hydrocarbon product containing formic acid and propionic acid and at least one of the butyric acids, the improvement which product with water until a large. proportion of the formic and acetic acids and a smaller procomprises Washing the portion of theV propionic =acids have been extracted, separating the resulting Water solution of these acids from the treated product, thereafter extracting the butyric acid from the treated product by Washing it with an aqueous alkaline solution, and separating the aqueous alkaline solution from the product.

WALLACE A. CRAIG.

PAUL C. RICH. 

